I had the same issue with the declarative-camera sample.
with QT 5.3 beta:
Camera video recording & image capture does work on a Galaxy S4 android phone (Android version 4.3 / kernel 3.4.0-2082040).
Image capture works on a Sony xperia android phone (Android version 4.0.4 / kernel 2.6.32.9-perf). But video recording doesn't work. I tried to downgrade the android API level to 15 in the declarative-camera project config, but it still reports "Media server died" when you press the record button.

Video Recording on iOS 7.0.4 (iPhone 5S) works after adding the others following plugins in the .pro file:
QTPLUGIN += qavfcamera qtaudio_coreaudio qavfmediaplayer
Thanks to this doc page: "qt-project.org/wiki/QtMultimedia_iOS":qt-project.org/wiki/QtMultimedia_iOS
The only remaining drawback is the video surface rendering freezes in the video recording mode (e.g: after you clicked the "switch to video" button). But the recording works and you can replay what you recorded with the "View" button.